1. Field of the Invention
This invention is directed to a method and an apparatus for the separation of gases by thermal cycling of a separation column. The method is accomplished with improved rapidity of cycling and without the necessity for pumps, blowers, and other mechanical means to effect heat transfer.
2. Background and Prior Art
The separation of isotopes has a long and frustrating history. Unlike other chemical separations isotopes show minimal differences in reactivity toward other chemical entities. Diffusion separators and centrifugal separators have been demonstrated to be highly effective but their costs are prohibitive except for highly visible nuclear power and/or military projects.
The separation of element number 1 into its three isotopes, 1H(protium or H), 2H(deuterium or D), and 3H(tritium or T) is important for studies in chemical kinetics and in medicine. The chemical properties of H, D, and T are essentially the same except for weight and equilibrium constants. The separation is made more difficult by the fact that the elements are normally found as the diatomic molecule and may exist in six different possible relationships.
Certain metal hydrides have been used for the storage of hydrogen and for the separation of the H, D, and T isotopes and these metals include vanadium, palladium, and uranium. U.S. Pat. No. 3,711,601 to Reilly et al. discloses a process for the use of vanadium hydride to concentrate and recover heavy hydrogen isotopes. U.S. Pat. No. 4,336,226 discloses a vanadium hydride gas generator to provide a D, T gas mixture in a pressurized chamber wherein the pressure is controlled by regulating the temperature of the high-pressure chamber.
U.S. Pat. No. 5,122,163 to Ide et al. discloses a method for isotope separation of gaseous isotopes in a thermal diffusion column having a hot wall and a cold wall.
U.S. Pat. No. 4,702,903 to Keefer discloses separating components of a gas mixture by thermal swing adsorption and/or pressure swing adsorption inside a Stirling cycle apparatus and absorbent bed.
U.S. Pat. Nos. 4,758,721 and 5,086,225 to Hill discloses isotope separation using thermal cycling in the context of a mass spectrometer. The objective is the concentration of iodine-123 for medical uses.
U.S. Pat. No. 4,859,427 to Konishi et al. discloses hydride-containing columns arranged in parallel within a sealed housing wherein heat is supplied by applying an electric current to heating coils within the housing. The reference attempts to address the problem of changes in the mechanical strength of the metal hydride as a result of generation of hydrogen gas by introducing a series of filters to maintain the integrity of the column.
U.S. Pat. No. 5,312,597 to Heung discloses an apparatus for separating and recovering hydrogen isotopes using a coil in a cylindrical housing as the separation column and externally supplied heating or cooling gases which alternatively heat and cool the column. The invention is particularly characterized by the use of an internal baffle to minimize the mass of the heating/cooling gas for a more rapid cycle time.
U.S. Pat. No. 5,505,829 to Villa-Aleman discloses an apparatus for the separation of the gaseous isotopes H, D, and T using molecular sieves. The apparatus is jacketed for cooling and the temperature of the mol sieves is cycled using microwave energy.
The efficiency of any process using thermal cycling or xe2x80x9cthermal swing adsorptionxe2x80x9d depends upon the rate at which the temperature can be raised and lowered to the optimal upper and lower operating temperatures. The prior art is characterized by low switching rates and by cumbersome supporting equipment and improvement has been long sought without success.
It is an object of this invention to improve the throughput of isotopic generators for H, D, and T. It is a further object of this invention to provide a method for maximizing the rate of isotopic separation at the lowest energy requirement. It is yet a further objective of this invention to provide a means for isotopic separation which requires a minimum amount of maintenance.
These and other objectives may be achieved by enclosing a separation column within a pressurized vessel containing a heating coil, a cooling coil, each of which may be enclosed separately in a structure which is insulated, valved to prevent backflow, and readily switched on and off.